It starts at 8 AM in most hotels. I think I've seen 7.45 or even 7.30 at DLH. Also I'm pretty sure I've seen longer times than 10 AM though in hotel New York. I got my photo taken with Daisy before the last pin event and that was definitely after 11.
The costumes sometimes vary - Goofy will for example wear a cowboy outfit in Hotel Cheyenne, but I've seen him in some uniform in Sequoia Lodge.